Pakistan's ambassador to Washington has been forced to resign after the
government ordered an investigation into claims he sought American help to
oust his country's military and intelligence chiefs.

Husain Haqqani finally resigned following a series of allegations by an influential Pakistani-American businessman who said he had passed a secret memo last May from the ambassador to Adml Mike Mullen, then America's most senior military chief, asking for US help to prevent a coup.

The businessman, Mansoor Ijaz, said the memo offered to install a "new national security team" and to dismantle sections of Pakistan's ISI intelligence service which supported terrorist groups in Afghanistan. It had been passed on with the blessing of President Asif Zardari, he suggested.

The disclosure of the memo provoked a crisis in the already tense relationship between Pakistan's elected government and its powerful military, which continues to control the country's defence spending budget and foreign policy.

Retired senior military figures said the Army chief General Kayani was furious over the claims and had demanded Mr Haqqani's resignation to settle the dispute.

Mr Haqqani had initially hoped to survive the controversy, but his position became increasingly untenable after General James Jones, the former American National Security Advisor, confirmed he had passed on the memo to Adml Mullen, the chairman of the Joint Chiefs of Staff.

It had been sent a week after the killing of Osama bin Laden in a raid by US Navy Seals on his home in the heart of Abbottabad, a heavily guarded Pakistan Army garrison town. The raid humiliated Pakistan Army chiefs who had not been warned and President Zardari was said to have feared they would mount a coup to restore morale.

Mr Haqqani's departure was confirmed in a statement by Yusuf Raza Gilani, the prime minister, who said he had asked for his resignation to allow a "detailed investigation" into the affair.

The inquiry was welcomed by Mr Haqqani who said it would "strengthen the hands of elected leaders whom I strove to strengthen."

Leading Pakistani commentator Cyril Almeida said the resignation highlighted the continuing power of the country's military establishment.

"What we are seeing is the reality of the imbalance between the civilian and military leaders and that the army will not give up any power," he said.